PEt 
ANATOMICAL RECORD 


Vol. III. JUNE, 1999. No. 6. 


I. CONCOMITANT ASSIMILATION OF THE ATLAS AND 
OCCIPUT WITH THE MANIFESTATION 
OF AN OCCIPITAL VERTEBRA. 


i NOTHS ON A HYPOCHORDAL BRACE. 
BY 


THOMAS DWIGHT, 
From the Department of Anatomy, Harvard Medical School. 


C 


bard 


IL. 

The simultaneous occurrence of fusion of the atlas and occiput, 
with the presence of a more or less distinct occipital vertebra, 1s 
of much importance in the discussion concerning the significance 
of numerical variations of the vertebral column. The observations 
by Zojat and Swjetschnikow” both deal with the manifestation of 
an occipital vertebra that is most developed in its anterior and lateral 
portions. Although we find vague allusions in lterature to the 
simultaneous occurrence of these two conditions, yet, so far as I know, 
these two anatomists are the only ones who have observed them. 
In point of fact it was the Russian who recognized the occipital ver- 


1Zoja, G. Intorno all’ atlante stude anthropo-zootomici. Con una tavola. 
Letture fatte nell adunanze 4 marzo, 4° aprile, 13 maggio, 17 giugno 1880 e 
19 maggio 1881. Pp. 269-296. 

2Swjetschnikow. Ueber die Assimilation des Atlas und die Manifestation 
des Occipitalwirbels beim Menschen. Arch. fiir Anat. u. Physiol, Anat. Abth. 
1906, pp. 155-193. 


(321) 


/P 50120 


322 Thomas Dwight. 


tebra in Zoja’s specimen. The case to be described in this paper 
differs from them in that the posterior arch of the occipital vertebra 
has a free point. Similar appearances have been found on isolated 
skulls, but, I believe this is the first time it has been seen when the 
atlas is fused. It makes the fact doubly sure to have the tree 
points of the imperfect posterior arches of the atlas and occipital 
vertebra appear in series one above the other (Fig. 1). This body 
presented other vertebral irregularities: a supra-sternal bone and 
(perhaps) a hypochordal brace of the axis (Fig: 5), Thes last 
feature is considered in the second division of this communication. 

These observations were made on the body of a white man, aet. 
50, dissected at the Harvard Medical School, in the season of 
1907-08. The skeleton was distinctly pathological, as is often the 
case with very exceptional vertebral variations. ‘Thus, the two cases 
which I have reported of 26 pree-sacral vertebree on one side and 
25 on the other were both extremely pathological.” ; 

The calvaria is a fine specimen of hyperostosis manifested on the 
inner table and especially in the frontal region, where it presents a 
hummocky surface with a maximum thickness of nearly 18 mm. 
Towards the posterior inferior parietal ay sle the thickness is about 
12 mm. The buccal surface of the hard palate presents a similar 
condition (Fig. 4). 

The vertebral formula is as follows, omitting any mention of the 
occipital vertebrae: C. 7, T. 18, L. 5, S. 5, 0.4. The atlas is fused 
with the oeciput, one might say absorbed into it, so far as some 
parts are concerned. The axis and third vertebra are fused, the 
fusion dating undoubtedly from early embryonic life (Figs. 2 and 
5). On the left the lateral portions of the two vertebra occupy 
their normal relations. On the right they are very close together. 
The lamin, though fused on the left, retain their distinctness, 
and the spinous process ends in two knobs, one above the other, 
each representing the lateral termination of the bifurcated spines of 
the two vertebrae, while on the right there is but one knob for the 


‘Dwight, Thomas. Description of the Human Spines Showing Numerical 
Variation in the Warren Museum of the Harvard Medical School. Memoirs 
of the Boston Soe. Nat. History, V, 287-312. 1901. 


Occipital Vertebra and Hypochordal Brace. 323 


two. The spines of the fourth, fifth and sixth cervical vertebrz are 
bifid. The laminz of the sixth vertebra present on each side a 
sharp point (Fig. 2, L.) rather less than 1 cm. from the spinous 
process. That on the left is the larger. The fifth vertebra presents 
a very small similar projection on the left side only. The bodies of 
the sixth and seventh cervical and first thoracic vertebrae are fused 
through prominent exostoses. This 1s evidently the result of a 
pathological process, and 1s accompanied with distortion of this re- 
gion, the details of which do not seem to the purpose. There are 
several projections on the ventral aspect of the bodies of the ver- 
tebree in the thoracic region which would ultimately have led to 
fusion, if they have not already done so, and one on the second 
fumbar vertebra. Apart from this last feature, the lumbar vertebree 
are normal, though the relative spread of their transverse processes 
is not that of a normal lumbar region. This is owing to the transi- 
tional character of the twentieth vertebra, which has been reckoned 
a thirteenth thoracic. The change in direction of the articular 
processes occurs below the twelfth thoracic. The costal elements of 
the twentieth vertebra are free, but insignificant. The right one 
measures 2.5 em., the left one 3.3 cm. It is really a matter of taste 
whether we say that there are thirteen thoracic vertebre and five 
lumbar, or twelve thoracic and six lumbar. The twelfth rib meas- 
ures 13.5 em. on the right and 14 em. on the left. There are seven 
sternal ribs on both sides. On the left the cartilage of the eleventh 
joins that of the tenth—it probably did not do so on the right. The 
twenty-sixth vertebra (first sacral) is the fulcralis, 1. é., the most 
important one in supporting the sacrum. The third sacral vertebra 
presents. a sudden change in the curve (Hermann von Meyer’s con 
jugata vera). The first coccygeal is fused with the sacrum. Thus, 
except in the last detail, the sacrum is perfectly normal, in spite of 
the increased number of vertebrae above it. The ensiform cartilage, 
ossified and fused with the body, is bifid below. The most remark- 
able feature of the sternum is a knob at the top of the posterior sur- 
face of the left half, at the median end of the clavicular notch. It 
is 6 mm. in height, tolerably clearly marked off, and suggests very 
strongly a supra-sternal bone fused with the manubrium. On the 


324 Thomas Dwight. 


right the sternum is prolonged upward perhaps a little more than 
usual, but presents no corresponding structure. 

The Occipital Region. ‘The anterior arch and lateral masses of 
the atlas are well developed, but it is so closely fused with the occiput 
that there is no sign of any occipital condyles. ‘There is a small 
interval between the anterior arch and the occiput and on either 
side of this a deep groove above the atlas. The height through the 
region of the articular processes is about 2 cm. on the right and 1.5 
em. on the left. Seen from the intracranial side the fusion is very 
complete. The left posterior arch is, in the main, well developed, 
quite free, ending in a point some 5 mm. from the median line 
(Fig. 4). This piece, which is now separate, was in life connected 
by cartilage to the atlas just external to the inferior articular process. 
The left vertebral artery grooved its superior surface. The repre-_ 
sentative of the right posterior arch of the atlas is a thin sliver of 
bone, the point of which had been broken off (Figs. 1, 3,4). It was 
less than 15 mm. in length when measured and probably never was 
more than 2 or 3 mm. longer. This was separated by a mere crack 
from the base of the skull at the border of the foramen magnum. The 
vertebral artery, smaller than the left one, j 1dging from the size otf 
the foramen in the axis, must have passed below this rudimentary 
arch. The lateral parts of the atlas differ very much on the two 
sides (Fig. 3). On the left, the costal element of the atlas is 


wanting, so that the transverse foramen is completely open in front, 


roy) 
except for a very slight hook projecting from the median side. The 
transverse process is strong, and ends in a knob which rests against 
the vaginal process of the temporal. On the right the lateral mass 
is inextricably mixed with the occiput. The transverse process is 
short and indistinct till near its end, which projects strongly back- 
ward; but a projection from near the end runs somewhat forward 
and is assimilated into an ill-marked paramastoid process. The 
groove already mentioned, anterior to the foramen magnum at the 
junction of atlas and occiput, has on the right a deeper part, which 
extends from the anterior condyloid foramen laterally to the en- 
trance to a canal between the transverse process and the skull, which 
runs antero-posteriorly. (It is unlikely that there was an sub- 


occipital nerve on the right.) 


Occipital Vertebra and Hypochordal Brace. 325 


There is an unquestionable manifestation of the posterior arch 
of an occipital vertebra on the right, and a less distinct one on the 
left. The right arch forms the boundary of the foramen magnum, 
but some 3 or 4 mm. before reaching the median line it ends in a 
‘point, which is separated from the bone above it by a sharp cleft 
some 3 mm. deep. This is seen most strikingly on the inner aspect 
(Fig. 1), but is clear also on the outside (Figs. 3 and 4). 


er Puke On OV2? 


Hie. 1. 


fey Agias. ~- OV... Manifestation of occipital vertepra. P.A.A., Posterior 
arch of atlas. ) 


On the right, close to the middle line, and nearer to it than the 
end of the occipital vertebra above described, there is a small knob 
which might be held to indicate the termination of another occipital 
vertebra above it (O. V. (?)). On the lower surface of the left 
posterior border of the foramen magnum there is a very fair mant- 
festation of the arch of an occipital vertebra, marked off by a 


groove. It ends rather vaguely some 2 or 3 mm. from the median 
line (Figs. 3 and 4, O. V.). | 


326 Thomas Dwight. 


The right anterior condyloid foramen 1s small. On the left it is 
subdivided into a larger lower and a smaller upper division by a 
tongue of bone projecting forward from behind and reaching the 
anterior border. This foramen opens into a groove, already alluded 
to, between the front of the atlas and the occiput. From the region 
of the condyle for some distance forward the borders of the occiptal 
bone grow downward so as to shut out the atlas from forming a 
part of the wall of the spinal canal, and placing it in the main in 
front of the occiput instead of below it. This is particularly marked 
on the left. Fig. 3 shows a deep vertical cleft between these bones 
on the interior surface. . 

Certain peculiarities are to be noted in the region of the odontoid, 
which is very long, measuring 19 mm. on the posterior surface, 
from the lower border of the facet for the transverse ligament to the 
top. The superior part of the odontoid (nearly one-half) is in the 
same vertical plane as the anterior surface, but does not reach back 
to the posterior one. Seen from behind this upper part is a rough- 
ened irregular piece of bone, giving a suggestion of an additional ele- 
ment (Fig. 2). A noteworthy point is the difference of position of 
the anterior and the posterior articular facets of the odontoid. In 
fact, the highest part of the posterior one does not extend above the 
level of the middle of the anterior one, which latter reaches to the 
very top of the odontoid. This is shown in Figs. 2 and 5. The 
superior articular facets of the axis slant perhaps a little more 
steeply than usual downward and outward, and the pedicles of the 
axis decline very steeply behind them. All this would imply that 
the head must have been carried with the chin high. When we 
consider the fusion, in some cases congenital and in others patho- 
logical, of so many of the cervical vertebra, it would seem that the 
power of nodding must have been nearly abolished. Presumably 
the joints above the axis allowed a great deal of irregular motion. 

Besides these manifestations of an occipital vertebra‘in the region 
of the foramen magnum, there is on the left side an apparent mani- 
festation of one seen from the front, made by modifications of the 
anterior border of the occipital bone, which is developed into a hori- 
zontal shelf where it bounds the jugular foramen, and, continued 


Occipital Vertebra and Hypochordal Brace. 327 


forward, forms the line marking off the groove above the anterior 
arch of the atlas. This manifestation is much less clear on the right. 


Jehitely 


L., Point on left lamina of 6th vertebra. 

Po Posterior articular facet. S2, Left lateral knob of spine of 2d vertebra. 
S3, Left lateral knob of spine of 3d vertebra. S4, Right knob resulting from 
the fusion of the right lateral knobs of the 2d and 3d vertebre. 


On the latter side a delicate process from the border of the occipital 
divides the exit of the venous canal from the nervous one (Fig. 3, 


at: : 


328 Thomas Dwight. 


This spine presents also a possible hypochordal brace which is 
considered in the second part of this paper. 

The following facts are to be noted in this case. The presacral 
vertebrae are increased by a transitional one between the thorax and 


OWS mm OVER 
gs 7el OA. 

ALA.” e--— PACA. 
or VE 
Beye ah eat ee hr 
—=C.C. 


Fic. 3. 


C.C., Carotid canal. J.F., Jugular foramen,—under the leader is the spicule 
dividing it. O.V., Manifestation of occipital vertebra. P.A.A.. Posterior 
arch of atlas. P.M., Paramastoid processes. H., Hook by transverse foramen 
of atlas. T.P., Left transverse process of atlas resting on vaginal process of 
temporal. 


loins, bearing short movable costal elements. The ribs on the 
vertebra above it are longer than is usual for last ribs. The second 
and third vertebrae are fused, the fusion of the arches being more 
intimate on the right. The atlas is fused much more intimately 
with the occiput on the right, and the right arch is much less devel- 


Occipital Vertebra and Hypochordal Brace. 329 


oped; yet the manifestation of the occipital vertebra, as shown by 
its free point, is more advanced on the same side. On the right, 
also, there is the hint of the presence of the point of the arch of still 
another occipital vertebra. The suggestion of the antero-lateral part 
of an occipital vertebra is more distinct on the left. 

It is much to be regretted that in so few cases of variations about 
the foramen magnum do we have an account of the entire column. 
Smith? remarks that “true assimilation of the atlas is rarely, if ever, 
an isolated anomaly of the cranio-vertebral axis.” There can be no 
doubt as to the correctness of this statement. In support of it Smith 
points out that the cases of Morgagni, Schiffner and Lambl had also 
fusion of the axis and the third vertebra; that in two other cases 
there were cervical ribs; and that a case of his had beside fusion 
of the axis and third vertebra, a cervical rib and other striking anoma- 
lies. To these I would add that among the spines in the Warren 
Museum showing numerical variation, there are three complete ones 
with fusion of the atlas and occiput, of which one must be discarded 
because the fusion is to be considered pathological, and one speci- 
men in which eight vertebra are preserved. The first (spine 561) 
has an extra vertebra at the junction of the back and loins, with small 
free costal elements, while the ribs of the twelfth thoracic are very 
long. The twenty-fifth vertebra is more or less sacralized on both 
sides. The next (spine 24) is very normal, only the arch of the 
last lumbar is distinct and there are certain distinct epiphyses ( ?) 
on the caudal side of some of the lumbar articular processes. I have 
excluded spine D-7 for the reason given. It has only four lumbar 
vertebre. The specimen which consists of the neck and the top of 
the thorax has suffered the loss of the left transverse process of the 
atlas, probably by accident. On the right the costal element is 
wanting. Presumably it was free and was lost. Just the same may 
be said of the right costal element of the seventh. The label states 
that the vertebral formula is believed to have been normal. It may 
be repeated that the spine which is described in this paper has an 


‘Smith, G. Elliot. The Significance of Fusion of the Atlas to the Occipital 
Bone, and Manifestation of Occipital Vertebrae. British Med. Journ., 1908, 
594-596. 


99 


33 Thomas Dwight. 


extra vertebra at the junction of back and loins and fusion of the 
axis and third, which last feature seems remarkably common in these 
cases. | 

We have known for centuries that the atlas may be assimilated 
more or less completely with the occiput, and for a few years we 
have accepted the manifestation of an occipital vertebra, usually 
an inseparable part of the occipital bone. The most perfect observa- 
tion is that recorded by v. Schumacher,’ who described several pieces 
of a fairly developed vertebra between the atlas and occiput, without 
bony connection with either. Recently we have had discussions as 
to whether certain “manifestations” on the bases of isolated skulls 
were to be considered as belonging to one region or to the other. 
Even without the light that is thrown on such peculiarities when 
the spine is present, we must recognize that the case is the same as 
at other transitional parts of the spinal column. A twenty-fifth 
vertebra may be a sacral vertebra or a lumbar vertebra, or a cross 
between the two. It may even be both at once in its two halves. 
Similar observations may be made at the two ends of the thorax. 
It is idle to discuss which vertebra a particular vertebra is. All 
we can say is which one it is like. I agree fully with Bateson 
that we must not treat the members of such a series as individuals. 
The details of their structure vary according to circumstances. 
Many years ago Topinard discussed at length which vertebra was 
wanting in a spine in which there were only eleven thoracie ones. 
We now know better; but it would seem that in discussing the oce1- 
pital region we are slow to apply the principles we follow else- 
where. 

The great importance of the present specimen is that it is one 
of the few undoubted cases of assimilation of the atlas and occiput, 
with manifestation of an occipital vertebra. Perhaps it is the 
only one. What is most remarkable is that both these processes have 
made the greatest progress on the same side. The cases of Zoja 
and Swjetschnikow each show connection between the skull and 
the spine by means of paramastoid processes from the skull and 


‘Schumacher, Siegmund v. Hin Beitrag zur Frage der Manifestation des 
Occipitalwirbels. Anat. Anz., XXXI, 1907, 145-159. 


(SU) 
= 


Occipital Vertebra and Hypochordal Brace. 3 


anomalous upgrowths to meet them from the transverse processes of 
the atlas. In the latter’s case there is a very slight ossification 
between the bones at one condyle, which probably is pathological. 
Now in both these cases the posterior arch of the atlas is apparently 
both free and well developed. Hence they appear to me to belong 
to a different class from those in which the body and _ posterior 


IPRA At OVO VEO ee PATA. 
1 4 ! 


1 1 ' ! 
| ; ! 1 


Fic. 4. 


P.A.A., Posterior arch of atlas. - O.V., Manifestation of occipital vertebra. 


arch of the atlas are more or less assimilated with the skull. IL 
regret that Swjetschnikow does not give a figure of his specimen, 
but he tells us that it is “demjenigen von Zoja dusserst ahnlich.” 
Although the use of color by the Russian anatomist on Zoja’s figure 
is hardly justifiable, as appealing too much to the imagination, it 
is not to be denied that the tubercle on the anterior border of the 


332 Thomas Dwight. 


foramen magnum points distinctly to the manifestation of an occi- 
pital vertebra of which other parts are indicated. The occipital 
vertebra must be admitted in these cases; but there is no real assimi- 
lation of the atlas and occiput. 


FIG. 5. ; 


11.B., Hypochordal brace. 


~The present specimen shows far more conclusively the presence in 
the same body and most markedly on the same side) of two dis- 
tinetly antagonistic processes, according to the popular theory which 
would have the one a return to the past and the other a step toward 


Occipital Vertebra and Hypochordal Brace. 333 


the future. It is therefore one more piece of evidence for the con- 
servative theory of variation around a mean. 


de. 


It remains to speak of the hypochordal brace (Fig. 5), if indeed 
that be its morphological significance. It is a stout ossification 
close on 15 mm. long, with the greatest breadth of some 7 mm. 
situated free on the front of the axis, its upper part somewhat over- 
lapping the lower border of the anterior articular surface of the 
odontoid. The anterior arch of the atlas presents a kind of a 
facet looking downward and forward, whl presumably locked — 
with its upper part. 

As to the significance of this element, it may be said in favor 
of its being nothing but an accidental ossification that the body was 
a distinctly pathological one, showing in many places a tendency 
to the proliferation of bone. This, in fact, is not to be denied. 
Nevertheless, the anterior surface of this ossicle has what one may 
call a “finished” appearance. Whether the fact of its upper dorsal 
surface being so shaped as to enable it to “lock” with the anterior 
arch of the atlas is of importance, is a question more easily asked 
than answered. The fact, however, that an ossification is occa- 
sionally found at this precise point speaks strongly for its having a 
morphological significance. Yet if it be an hypochordal brace, it 
can be only that of the axis, and embryology leaves one in doubt 
whether this explanation is legitimate. There is indeed such a car- 
tilaginous anlage, but according to Bardeen it is very transient. 
This spine is so abnormal, showing so many irregularities that must 
have occurred at a very early period, that it seems favorable soil 
for such an unexpected growth; but F have recently seen another 
instance of this ossification, though a smaller one, in a spine which, 
if not quite normal, was not remarkable. 

Just before revising the proof of this paper I received the Ana- 
tomischer Anzeiger of May 5, 1909, containing Smith’s case of fusion 
of atlas and occiput with the manifestation of an occipital vertebra. 


NINN NO 


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